如何将相机居中以使标记位于屏幕底部？ (谷歌地图api V2 Android)

Question

When a marker is clicked, the default behavior for the camera is to center it on screen, but because I usually have long text description in the info window, it's more convenient to actually change the camera position so that the marker is on the bottom of screen(making the info window in the center of screen). I think I should be able to do that by overriding onMarkerClick function like below (the default behavior is cancelled when this function return true)

@Override

public boolean onMarkerClick(final Marker marker) {


    // Google sample code comment : We return false to indicate that we have not

    // consumed the event and that we wish
    // for the default behavior to occur (which is for the camera to move
    // such that the
    // marker is centered and for the marker's info window to open, if it
    // has one).

    marker.showInfoWindow();

            CameraUpdate center=
                CameraUpdateFactory.newLatLng(new LatLng(XXXX,
                                                         XXXX));
            mMap.moveCamera(center);//my question is how to get this center

            // return false;
    return true;
}

Edit:

Problem solved using accepted answer's steps, codes below:

@Override

    public boolean onMarkerClick(final Marker marker) {

                //get the map container height
        LinearLayout mapContainer = (LinearLayout) findViewById(R.id.map_container);
        container_height = mapContainer.getHeight();

        Projection projection = mMap.getProjection();

        LatLng markerLatLng = new LatLng(marker.getPosition().latitude,
                marker.getPosition().longitude);
        Point markerScreenPosition = projection.toScreenLocation(markerLatLng);
        Point pointHalfScreenAbove = new Point(markerScreenPosition.x,
                markerScreenPosition.y - (container_height / 2));

        LatLng aboveMarkerLatLng = projection
                .fromScreenLocation(pointHalfScreenAbove);

        marker.showInfoWindow();
        CameraUpdate center = CameraUpdateFactory.newLatLng(aboveMarkerLatLng);
        mMap.moveCamera(center);
        return true;



    }

Thanks for helping ^ ^

Answer 1

I might edit this answer later to provide some code, but what I think could work is this:

1. Get LatLng ( LatLng M ) of the clicked marker.
2. Convert LatLng M to a Point ( Point M ) using the Projection.toScreenLocation(LatLng) method. This gives you the location of the marker on the device's display (in pixels).
3. Compute the location of a point ( New Point ) that's above Point M by half of the map's height.
4. Convert the New Point back to LatLng and center the map on it.

Look here for my answer on how to get the map's height.

    // googleMap is a GoogleMap object
    // view is a View object containing the inflated map
    // marker is a Marker object
    Projection projection = googleMap.getProjection();
    LatLng markerPosition = marker.getPosition();
    Point markerPoint = projection.toScreenLocation(markerPosition);
    Point targetPoint = new Point(markerPoint.x, markerPoint.y - view.getHeight() / 2);
    LatLng targetPosition = projection.fromScreenLocation(targetPoint);
    googleMap.animateCamera(CameraUpdateFactory.newLatLng(targetPosition), 1000, null);

Answer 2

Yes, use Projection class. More specifically:

Get Projection of the map:

 Projection projection = map.getProjection();

Get location of your marker:

 LatLng markerLocation = marker.getPosition();

Pass location to the Projection.toScreenLocation() method:

 Point screenPosition = projection.toScreenLocation(markerLocation);

Like this you can move your marker relative to center or around the screen

Point mappoint = googleMap.getProjection().toScreenLocation(new LatLng(latitude, longitude));
        mappoint.set(mappoint.x, mappoint.y-30);
        googleMap.animateCamera(CameraUpdateFactory.newLatLng(googleMap.getProjection().fromScreenLocation(mappoint)));

Answer 3

I prefer Larry McKenzie's answer which it doesn't depend on screen projection (ie mProjection.toScreenLocation()), my guess is the projection resolution will go poor when the map zoom level is low, it made me sometimes couldn't get an accurate position. So, calculation based on google map spec will definitely solve the problem.

Below is an example code of moving the marker to 30% of the screen size from bottom.

zoom_lvl = mMap.getCameraPosition().zoom;
double dpPerdegree = 256.0*Math.pow(2, zoom_lvl)/170.0;
double screen_height = (double) mapContainer.getHeight();
double screen_height_30p = 30.0*screen_height/100.0;
double degree_30p = screen_height_30p/dpPerdegree;      
LatLng centerlatlng = new LatLng( latlng.latitude + degree_30p, latlng.longitude );         
mMap.animateCamera( CameraUpdateFactory.newLatLngZoom( centerlatlng, 15 ), 1000, null);

Answer 4

If you don't care about the map zooming in and just want the marker to be at the bottom see below, I think it's a simpler solution

double center = mMap.getCameraPosition().target.latitude;
double southMap = mMap.getProjection().getVisibleRegion().latLngBounds.southwest.latitude;

double diff = (center - southMap);

double newLat = marker.getPosition().latitude + diff;

CameraUpdate centerCam = CameraUpdateFactory.newLatLng(new LatLng(newLat, marker.getPosition().longitude));

mMap.animateCamera(centerCam);

Answer 5

I had the same issue, I tried the following perfectly working solution

mMap.setOnMarkerClickListener(new OnMarkerClickListener() 
        {
            @Override
            public boolean onMarkerClick(Marker marker)
            {
                int yMatrix = 200, xMatrix =40;

                DisplayMetrics metrics1 = new DisplayMetrics();
                getWindowManager().getDefaultDisplay().getMetrics(metrics1);
                switch(metrics1.densityDpi)
                {
                case DisplayMetrics.DENSITY_LOW:
                    yMatrix = 80;
                    xMatrix = 20;
                    break;
                case DisplayMetrics.DENSITY_MEDIUM:
                    yMatrix = 100;
                    xMatrix = 25;
                    break;
                case DisplayMetrics.DENSITY_HIGH:
                    yMatrix = 150;
                    xMatrix = 30;
                    break;
                case DisplayMetrics.DENSITY_XHIGH:
                    yMatrix = 200;
                    xMatrix = 40;
                    break;
                case DisplayMetrics.DENSITY_XXHIGH:
                    yMatrix = 200;
                    xMatrix = 50;
                    break;
                }

                Projection projection = mMap.getProjection();
                LatLng latLng = marker.getPosition();
                Point point = projection.toScreenLocation(latLng);
                Point point2 = new Point(point.x+xMatrix,point.y-yMatrix);

                LatLng point3 = projection.fromScreenLocation(point2);
                CameraUpdate zoom1 = CameraUpdateFactory.newLatLng(point3);
                mMap.animateCamera(zoom1);
                marker.showInfoWindow();
                return true;
            }
        });

Answer 6

I did a little research and according to the documentation the map is square and at zero zoom level the width and height is 256dp and +/- 85 degrees N/S. The map width increases with zoom level so that width and height = 256 * 2N dp. Where N is the zoom level. So in theory you can determine the new location by getting the map height and dividing it by 170 total degrees to get dp per degree. Then get the screen height (or mapview height) in dp divided it by two and convert half view size to degrees of latitude. Then set your new Camera point that many degrees of latitude south. I can add code if you need it but I'm on a phone at the moment.

Answer 7

I also faced this problem and fixed it in a hacky way. Let's declare a double field first. You need to adjust the value of it based on your requirement but I recommend you keep it between 0.001~0.009 otherwise you can miss your marker after the zoom animation.

  double offset = 0.009 
  /*You can change it based on your requirement.
 For left-right alignment please kindly keep it between 0.001~0.005 */

For bottom-centered:

    LatLng camera = new LatLng(marker.getPosition().latitude+offset , marker.getPosition().longitude);
//Here "marker" is your target market on which you want to focus

For top-centered:

LatLng camera = new LatLng(marker.getPosition().latitude-offset , marker.getPosition().longitude);

For left-centered:

LatLng camera = new LatLng(marker.getPosition().latitude, marker.getPosition().longitude+offset);

For right-centered:

LatLng camera = new LatLng(marker.getPosition().latitude-offset , marker.getPosition().longitude-offset);

Then finally call the -

mMap.animateCamera(CameraUpdateFactory.newLatLngZoom(camera, yourZoom));

Answer 8

I have been trying out all the solutions proposed here, and came with a combined implementation of them. Considering, map projection, tilt, zoom and info window height.

It doesn't really place the marker at the bottom of the "camera view", but I think it accommodates the info window and the marker centre pretty well in most cases.

@Override
public boolean onMarkerClick(Marker marker) {
    mIsMarkerClick = true;
    mHandler.removeCallbacks(mUpdateTimeTask);
    mLoadTask.cancel(true);
    getActivity().setProgressBarIndeterminateVisibility(false);
    marker.showInfoWindow();
    Projection projection = getMap().getProjection();
    Point marketCenter = projection.toScreenLocation(marker.getPosition());
    float tiltFactor = (90 - getMap().getCameraPosition().tilt) / 90;
    marketCenter.y -= mInfoWindowAdapter.getInfoWindowHeight() / 2 * tiltFactor;
    LatLng fixLatLng = projection.fromScreenLocation(marketCenter);

    mMap.animateCamera(CameraUpdateFactory.newLatLng(fixLatLng), null);

    return true;
}

And then, your custom adapter would have to keep an instance of the info window inflated view, to be able to fetch its height.

public int getInfoWindowHeight(){
    if (mLastInfoWindoView != null){
        return mLastInfoWindoView.getMeasuredHeight();
    }
    return 0;
}

Answer 9

Anyone who's still looking to center the camera according to location coordinates

CameraPosition cameraPosition = new CameraPosition.Builder().target(new LatLng(Lat, Lon))
        .zoom(15) 
        .bearing(0)
        .tilt(45)
        .build();
    map.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));

Credits

Answer 10

After some experiences i've implemented the solution that fine for me.

DisplayMetrics metrics = new DisplayMetrics();
context.getWindowManager().getDefaultDisplay().getMetrics(metrics);

Point targetPoint = new Point(metrics.widthPixels / 2, metrics.heightPixels - metrics.heightPixels / 9);
LatLng targetLatlng = map.getProjection().fromScreenLocation(targetPoint);
double fromCenterToTarget = SphericalUtil.computeDistanceBetween(map.getCameraPosition().target, targetLatlng);

LatLng center = SphericalUtil.computeOffset(new LatLng(location.latitude, location.longitude), fromCenterToTarget/1.2, location.bearing);
CameraUpdate camera = CameraUpdateFactory.newLatLng(center);
map.animateCamera(camera, 1000, null);

Here. First, we pick the physical point on the screen where the marker should be moved. Then, convert it to LatLng. Next step - calculate distance from current marker position (in center) to target. Finally, we move the center of map straight from the marker to calculated distance.

Answer 11

I needed something similar, but with also zoom, tilt and bearing in the equation.

My problem is more complex, but the solution is a sort of generalization so it could be applied also to the problem in the question.

In my case, I update programmatically the position of a marker; the camera can be rotated, zoomed and tilted, but I want the marker always visible at a specific percentage of the View height from the bottom. (similar to the car marker position in the Maps navigation)

The solution:

I first pick the map location on the center of the screen and the location of a point that would be visible at a percentage of the View from the bottom (using map projection); I get the distance between these two points in meters, then I calculate a position, starting from the marker position, moving for the calculated distance towards the bearing direction; this new position is my new Camera target.

The code (Kotlin):

val movePointBearing =
      if (PERCENTAGE_FROM_BOTTOM > 50) {
          (newBearing + 180) % 360
      } else newBearing

val newCameraTarget = movePoint(
       markerPosition,
       distanceFromMapCenter(PERCENTAGE_FROM_BOTTOM),
       markerBearing)

with the movePoint method copied from here: https://stackoverflow.com/a/43225262/2478422

and the distanceFromMapCenter method defined as:

fun distanceFromMapCenter(screenPercentage: Int): Float {
    val screenHeight = mapFragment.requireView().height
    val screenWith = mapFragment.requireView().width
    val projection = mMap.projection
    val center = mMap.cameraPosition.target
    val offsetPointY = screenHeight - (screenHeight * screenPercentage / 100)
    val offsetPointLocation = projection.fromScreenLocation(Point(screenWith / 2, offsetPointY))
    return distanceInMeters(center, offsetPointLocation)
}

then just define a distanceInMeters method (for example using android Location class)

I hope the idea is clear without any further explanations.

One obvious limitation: it applies the logic using the current zoom and tilt, so it would not work if the new camera position requires also a different zoom_level and tilt.